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Two earthquakes 13 minutes apart shake the East Bay

A 4.4-magnitude earthquake struck 7.5 miles east of Blackhawk, according to the U.S. Geological Survey.

A 4.4-magnitude earthquake struck 7.5 miles east of Blackhawk, according to the U.S. Geological Survey.

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Photo: Leaflet, Carto

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A 4.4-magnitude earthquake struck 7.5 miles east of Blackhawk, according to the U.S. Geological Survey.

A 4.4-magnitude earthquake struck 7.5 miles east of Blackhawk, according to the U.S. Geological Survey.

Photo: Leaflet, Carto

Two earthquakes 13 minutes apart shake the East Bay

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A pair of earthquakes jolted East Bay residents Tuesday afternoon, raising concerns that more, bigger tremors are on the way, like the ones Southern California experienced two weeks ago.

A 4.3-magnitude quake struck between Blackhawk and Brentwood at 1:11 p.m., followed by a 3.5-magnitude shaker 13 minutes later, according to the United States Geological Survey.

No damage or injuries were reported, but residents in Martinez, Pittsburg and as far west as Berkeley reported light shaking. Experts at the Geological Survey calculated that there is a 4% chance of a similarly sized or larger earthquake in the same area over the next week.

“We should expect to see small aftershocks, but there is a lot of uncertainty” about that, said Keith Knudsen, deputy director of the Earthquake Science Center at the U.S. Geological Survey in Menlo Park. “There is always the possibility that it will lead to a larger earthquake, but it’s a low probability.”

The epicenter of the 4.3 quake was 7.58 miles below ground. The two quakes follow a 3.5-magnitude shaker north of Morgan Hill, in Santa Clara County, on Monday afternoon. Knudsen said the East Bay quakes are notable only because they are rare. Only two other quakes bigger than magnitude 3 have hit within 6 miles of Tuesday’s jiggling in the past 20 years, he said.

He nevertheless characterized the recent seismic activity as “business as usual.”

“The Bay Area has a series of faults that all slip and behave similarly,” Knudsen said. “Most of them produce earthquakes of this size pretty regularly.”

He said none of the local quakes are related to the 6.4- and 7.1-magnitude double whammy that slammed the high desert region of Ridgecrest, in Southern California, July 4 and 5. Since then, more than 8,900 tremors have jiggled the region, putting Californians on high alert.

“That was an interesting sequence of earthquakes, and we hope it is winding down,” Knudsen said. “It’s really just a reminder we live in earthquake country. Rather than be worried, take those precautions we all should be taking to make our families safe.”

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